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Date: Mon, 17 Jun 2013 03:57:26 -0700 (PDT)
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Subject: Range check for type 'Integer'
From: Peter Brooks <peter.h.m.brooks@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:15772
Date: 2013-06-17T03:57:26-07:00
List-Id: <comp.lang.ada>

I may be confused about this, but I don't understand the behaviour of
a very simple Ada program.

Firstly, this program does what I do expect:

"
procedure Compute_Loop is
type fred is range -3276732787230772307 .. 3276732787230772307;

 procedure Double(Item : in out fred) is
 begin -- procedure Double.
   Item := Item * 2;
 end Double;

 X : fred := 1;   -- Local variable X of type fred.

begin -- procedure Compute_loop
 loop
  Put("This is ");
  Put(Integer(X));
  New_Line;
  Double(X);
 end loop;
end Compute_Loop;
"

Output:

...
This is   268435456
This is   536870912
This is  1073741824
This is

raised CONSTRAINT_ERROR : compute_loop.adb:19 range check failed

Exactly the same program, but using type 'Integer' instead for 'fred'
gives:


...
This is   134217728
This is   268435456
This is   536870912
This is  1073741824
This is -2147483648
This is           0
This is           0
This is           0
This is           0
This is           0
This is           0
This is           0
This is           0
..... [forever]

So the 'Integer' has rolled over to negative and then rolled back to 0
- but with no run-time error.

Why is there no range check error on type Integer?